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Latent Prints

The Latent Print Section responds to crime scenes and offers crime scene support to law enforcement officials. The section is responsible for collecting, preserving, processing and examining physical evidence for the presence of footwear and tire impressions, fingerprints, palm prints, footprints and physical match. The section also instructs courses on photography, crime scene processing, and fingerprint.

Fingerprints, Palm Prints and Footprints

The word "latent" means invisible. Many times, impressions left at crime scenes are not visible and enhancement methods are utilized to render these impressions visible. Enhancement methods include: powders that adhere to the print residue, chemicals that react with the print residue and therefore turn a color, chemicals that harden the fingerprint residue thus preserving it and chemicals that dye stain the treated print residue.

The method chosen to enhance the prints depends on several factors including the type of surface the print is on and what the print is made out of. Surfaces vary greatly and will therefore hold a fingerprint differently; a sticky surface will hold a print differently than a bloody surface. Prints can be made out of many substances including grease, blood, dirt and dust but most prints are made of oils and sweat excreted from the pores of our bodies. Because prints are made of many different substances and can be on many different surfaces, a latent print examiner must choose the most appropriate means to develop that print. Many times, multiple enhancement techniques are utilized in a controlled sequence of steps. Alternative light sources are often used to search for and visualize prints.

Latent Prints Lab Image #1

Photography is used to document developed prints and is also often used as an enhancement method. A recent technique that has been adopted by the Latent Print section to enhance prints is the use of computer software such as Adobe Photoshop.

Once a print is developed, it is analyzed to determine if it is clear enough and has enough detail for a comparison. If it is determined to be suitable for comparison, the unknown (crime scene) impression is compared, side-by-side, to a known inked impression. A determination is then made as to whether both prints, the known and the crime scene print, were made by the same source.

Automated Fingerprint Identification System (AFIS):

The Latent Print Section compares the developed unknown latent impressions to known inked impressions and searches latent fingerprint impressions in the Automated Fingerprint Identification System (AFIS). The AFIS database consists of over 500,000 criminal fingerprint cards from Maine, New Hampshire and Vermont.

Contrary to what is "seen on TV", AFIS doesn't madly search a database of fingerprint entries and flash "match" in bold letters when a fingerprint is found. Nor does AFIS give us the name, address, date of birth or any information about the person who belongs to the fingerprint.

In reality, AFIS (Automated Fingerprint Identification System) is a computer-based, filing cabinet of known fingerprints. The Maine State Bureau of Identification maintains this "file cabinet". When an unknown fingerprint is developed at a scene or on a piece of evidence, it can be searched through AFIS. AFIS then generates a report of the top 50 fingerprints in the "file cabinet" that are similar to the unknown fingerprint. The latent print examiner then goes through each candidate given by AFIS and if a particular fingerprint looks very similar to the unknown fingerprint, the examiner then requests that fingerprint (on the fingerprint card) from the State Bureau of Identification and does a normal, side-by-side comparison between the actual unknown and the known prints. The only information AFIS gives on candidate fingerprints is the "State Identification Number" which leads to the actual known fingerprint card.

AFIS has been very beneficial in identifying remains and has helped several investigators with leads on suspects. However, due to the nature of the AFIS database, if a "hit" isn't generated from an AFIS search, that doesn't mean the fingerprint is not in the database. For this reason, law enforcement officials are cautioned not to rely on AFIS, even if they think their suspect has been arrested before. If there is a suspect, make sure you get known fingerprints (and we suggest major case prints) and send them the lab.